Abstract:

A method is provided for sensing leakage in a clutch cylinder system in a
vehicle including an automated manual transmission, wherein the clutch
cylinder system includes a clutch cylinder provided with a reciprocable
piston, whose position is sensed by a position sensor and affected by
pressurization of the cylinder by opening or closing at least one air
inlet valve and by opening or closing at least one air outlet valve and
wherein the clutch is in an engaged position when there is no air
pressure in the cylinder. The method includes the steps of: a. closing
the at least one inlet valve and at least one outlet valve for compressed
air; b. sensing a position of the piston during a predetermined time
span, and, c. if the position has changed more than a predetermined
allowable position change, sending an error signal to an onboard
diagnostics system or a signal light in the vehicle.

Claims:

1. Method for sensing leakage in a clutch cylinder system in a vehicle
comprising an automated manual transmission, wherein the clutch cylinder
system comprises a clutch cylinder provided with a reciprocable piston,
whose position is sensed by a position sensor and affected by
pressurization of the cylinder by opening or closing at least one air
inlet valve and by opening or closing at least one air outlet valve and
wherein the clutch is in an engaged position when there is no air
pressure in the cylinder, the method comprisingclosing the at least one
inlet valve and at least one outlet valve for compressed air;sensing a
position of the piston during a predetermined time span, andif the
position has changed more than a predetermined allowable position change,
sending an error signal to an onboard diagnostics system or a signal
light in the vehicle.

2. The method of claim 1, comprising the further steps of: at least partly
pressurizing the clutch cylinder prior to closing the at least one inlet
valve and at least one outlet valve for compressed air and if the
position has changed more than a predetermined allowable position change
in a negative direction, sending a second error signal to the onboard
diagnostics system or the signal light in the vehicle, wherein the second
error signal means there is a leakage in the clutch cylinder or the at
least one air outlet valve.

3. The method of claim 1, wherein the method is performed at temperatures
above a predetermined lowest air or gearbox temperature.

4. The method of claim 1, wherein there are provided two inlet valves and
two outlet valves leading compressed air to and from the clutch cylinder,
respectively.

5. The method of claim 1, wherein the predetermined allowable position
corresponds to 20% of the distance between a first piston position
wherein the clutch is fully engaged and a second position wherein the
clutch is fully disengaged.

6. The method of claim 1, wherein one inlet valve is larger than the other
inlet valve.

7. The method of claim 1, wherein one outlet valve is larger than the
other outlet valve.

Description:

[0001]The present invention relates to a method for sensing leakage in a
clutch cylinder system in a vehicle comprising an automated manual
transmission. The clutch cylinder system comprises a clutch cylinder
provided with a reciprocable piston, whose position is sensed by a
position sensor and affected by pressurization of said cylinder by
opening or closing at least one air inlet valve and by opening or closing
at least one air outlet valve and wherein the clutch is in an engaged
position when there is no air pressure in said cylinder.

[0002]In recent years, a new type of transmission system for trucks has
come into widespread use, namely the so called Automatic Manual
Transmission, or AMT. An AMT can basically be described as resembling an
automatic transmission, but includes no torque converter. An AMT
generally comprises an electronically controlled gearbox, and an
electronically controlled clutch. There is no clutch pedal in the
vehicle.

[0003]Usually, both the clutch and the gearbox are powered by compressed
air. The electronic control system controls the amount and rate of
compressed air entering and leaving control cylinders controlling the
clutch and gearbox.

[0004]Usually, the clutch cylinder is provided with one large diameter and
one small diameter inlet valve and one large diameter and one small
diameter outlet valve. By controlling the valves, rapid or slow
engagement and disengagement of the clutch can be achieved, partly by
choosing which valve should be opened, partly by using different "duty
cycles" for the valves, e.g. by pulse width modulation.

[0005]Usually, the clutch cylinder is provided with a position sensor for
sensing the position of the clutch. This is an important feature, since
it allows for a fast and precise control of the clutch position, and
thereby the amount of torque the clutch can transfer, and further for
adjustment.

[0006]During operation, the control system controlling the gearbox and
clutch demands a clutch position. Responsive to the demand, the control
system opens and closes the inlet and/or outlet valves to put the clutch
cylinder in the demanded position.

[0007]One feature with such a system is that the system automatically
compensates for leakages in the clutch cylinder or its air supply system.
This feature is of course beneficial in that it is possible to continue
to operate the vehicle. However, in many cases the driver of the vehicle
will not notice a minor leakage and since a minor leakage might lead to a
larger leakage, this non-notice of the leakage might pose a problem.

[0008]According to an aspect of the present invention, the above problems
are solved by a method for sensing leakage in a clutch cylinder system in
a vehicle comprising an automated manual transmission. The clutch
cylinder system comprises a clutch cylinder provided with a reciprocable
piston, whose position is sensed by a position sensor and affected by
pressurization of said cylinder by opening or closing at least one air
inlet valve and by opening or closing at least one air outlet valve. The
clutch is in an engaged position when there is no air pressure in said
cylinder. The method comprises the steps of: [0009]1. closing said at
least one inlet valve and at least one outlet valve for compressed air;
[0010]2. sensing a position of said piston during a predetermined time
span, and [0011]3. if the position has changed more than a predetermined
allowable position change, sending an error signal to an onboard
diagnostics system or a signal light in the vehicle.

[0012]Note that the cylinder could be pressurized or not pressurized
during said above steps.

[0013]In a preferred embodiment of the invention, the method comprises the
further steps of: at least partly pressurizing the clutch cylinder prior
to closing said at least one inlet valve and at least one outlet valve
for compressed air and if the position has changed more than a
predetermined allowable position change in a negative direction, sending
a second error signal to the onboard diagnostics system or the signal
light in the vehicle, wherein the second error signal means there is a
leakage in said clutch cylinder or the at least one air outlet valve.

[0014]By the above preferred embodiment of the invention, it is possible
to determine leakage of pressurized air from the clutch cylinder or
through the outlet valves.

[0015]Due to the fact that material shrinkage and loss of resilience make
even flawless clutch cylinders leak at low temperatures, the method is
preferably only performed at temperatures above -25 degrees C.

[0016]In order to provide possibilities for rapid engagement and
disengagement of the clutch, there could be two inlet valves and two
outlet valves leading compressed air to and from the clutch cylinder,
respectively.

[0017]In a preferred embodiment of the invention, the predetermined time
is about 30 seconds and the predetermined allowable position change is
about 20% of the distance between a fully engaged and a fully disengaged
clutch.

[0018]In order to further increase the controllability of the clutch
cylinder, one inlet valve could be larger than the other inlet valve. For
the same reason, one outlet valve could be larger than the other outlet
valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]Hereinafter, the invention will be described with reference to the
only drawing, FIG. 1, which schematically shows an exemplary clutch
cylinder arrangement for which the claimed method could be used.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0020]With reference to FIG. 1, a clutch cylinder 110 having a piston 115
is connected, via a lever 120, to disengage a clutch C upon
pressurization with compressed air from a source 130. The pressurization
of the clutch cylinder 110 is controlled by four valves V1, V2, V3, V4,
wherein the valve V1 is a large diameter inlet valve, valve V2 is a small
diameter inlet valve, valve V3 is a large diameter outlet valve and valve
V4 is a small diameter outlet valve. The valves V1 and V2 are arranged to
control inlet of compressed air from the source 130 into the clutch
cylinder 110. The valves V3 and V4 are used to control outflow of
compressed air from the clutch cylinder to the atmosphere A. By the
valves V1, V2, V3 and V4, it is possible to engage and disengage the
clutch C slowly or rapidly, simply by controlling which valve that should
be open; the fastest clutch disengagement is achieved by opening both
inlet valves V1 and V2 simultaneously, a somewhat slower disengagement is
achieved by opening only the large diameter inlet valve V2, an even
slower disengagement by opening only the small diameter valve V2, and the
slowest clutch disengagement by pulse width modulating the small diameter
valve V2 to open and close periodically during one disengagement
sequence.

[0021]The clutch can be engaged in a similar manner, but for engagement,
the valves V3 and V4 are opened instead, wherein the fastest engagement
is achieved by opening both the outlet valves V3 and V4, and the slowest
engagement is achieved by pulse width modulation of the small diameter
outlet valve V4 to open and close periodically during an engagement
sequence.

[0022]As can be understood by persons skilled in the art, an increased
pressure in the cylinder 110 biases the piston 115 to the right in FIG.
1. Oppositely, a decreased pressure in the cylinder 110 will make the
piston 115 to move in the other direction, i.e. towards the left in FIG.
1, since the clutch C urges towards an engaged position; the engaged
position is the resting position of the clutch.

[0023]A position sensor 140, e.g. of inductive type, is arranged to sense
the position of the piston 115. By the position sensor, it is possible to
adjust a disengagement stroke of the piston 115 responsive to clutch
wear. In an exemplary embodiment of the invention, the piston stroke from
fully engaged clutch to fully disengaged clutch is 25 mm. However, the
position where the clutch is fully engaged, will move responsive to
clutch wear. By the position sensor, it is possible to minimize the
piston stroke from fully engaged clutch to fully disengaged clutch to 25
mm. Minimizing the piston stroke is advantageous from many points of
view; firstly, air consumption is minimized and secondly, the necessary
time for clutch engagement/disengagement is minimized.

[0024]The valves V1, V2, V3 and V4, and the position sensor 140 are
connected to a controller (not shown). This controller might also be
connected to one or more of an automated manual gearbox (not shown), a
brake sensor (not shown) sensing a brake pedal position, a gas pedal
sensor (not shown) sensing a gas pedal position, a speed sensor (not
shown) sensing a vehicle speed, a temperature sensor (not shown) sensing
outside temperature and an accelerometer (not shown) sensing vehicle
acceleration. Responsive to information from these sensors, the
controller orders a proper gear to the gearbox and a proper movement of
the piston 115, in order to engage and disengage the clutch.

[0025]If a leakage of compressed air would occur, the system could be
adapted for noticing this by a change in the ratio of the movement of the
piston 115 versus the opening times of the valves V1-V4. Initial tests
have however shown that it is difficult to make such a system to function
in a very secure manner, since hysteresis effects in the system, e.g.
from friction phenomena, make it very difficult to sense a leakage by a
shift in the valve opening times vs. piston movement. Moreover, there are
vehicle individual differences, like e.g. different compressed air
pressures and clutch spring ratios due to wear, that affects the ratio of
the movement of the piston 115 versus the opening times of the valves
V1-V4.

[0026]According to the invention, leakage in the clutch cylinder system is
detected by a monitoring clutch cylinder movement when all inlet and
outlet air valves are closed.

[0027]According to the invention, a leakage test is performed at a certain
rate, e.g. one time after each key-on. A first test, determining leakage
in the inlet valves V1 and/or V2, could be carried out as follows:

[0028]In a first step, all valves V1-V4 are closed; in a second step, the
position of the piston 115 is monitored by the position sensor 140.
Should the piston move more than a predetermined distance (e.g. 20% of
the distance from a position corresponding to fully engaged clutch to a
position corresponding to fully disengaged clutch) during a predetermined
time span (e.g. 30 seconds), the controller determines that there is a
leakage from the clutch cylinder 110.

[0029]In an optional step, used to determine leakage from the clutch
cylinder 110 or through the outlet valves V3 and/or V4, the cylinder is
at least partly pressurized prior to performing the above described first
test.

[0030]In a preferred embodiment of the invention, the controller
determines whether there is a leakage of air from the cylinder or into
the cylinder by sensing the direction of the position change of the
piston (115). The result is preferably stored in a memory in the
controller, for subsequent readout at a service station or workshop. Such
memories in, or in connection to, controllers, are generally referred to
as onboard diagnostics systems, or OBD systems.

[0031]If the controller would determine that there is a leakage of
compressed air from or into the clutch cylinder, the controller might
transmit this in some different ways:

[0032]In a first transmittal embodiment, the controller might flash a
signal light (not shown) on a dashboard of the vehicle. This may however
not be advantageous, since warning lights on the dashboard generally
means that the vehicle error which is signaled requires immediate
attention. This is not the case for a minor clutch cylinder leakage.

[0033]In a second transmittal embodiment, the controller might save a
clutch cylinder error code in an onboard diagnostic system (OBD system,
not shown). The OBD system could be read out during a coming service at a
workshop, and proper repair work, control or replacement of damaged parts
could be conducted at the service.

[0034]At cold outside temperatures (e.g. below -20 degrees C.), the clutch
cylinder will leak air, even if there is no actual malfunction of the
cylinder. This is due to the fact that material shrinkage and/or loss of
gasket and sealing resilience occur at such low temperatures. In order
not to receive any "false" determinations regarding clutch cylinder
leakage, testing of clutch cylinder leakage could be discarded below
temperatures of e.g. 0 degrees C.

[0035]In the description, the piston 115 acts upon the clutch C by the
lever 120 in a so-called pull-type clutch arrangement. In some
embodiments, the piston acts directly upon a clutch diaphragm spring onto
which the pressure plate is attached, which is a so-called push-type
clutch arrangement.

[0036]Moreover, the described embodiment uses four different valves V1-V4.
This is however not necessary for carrying out the invention. In another
embodiment, there is only one inlet valve and one outlet valve connected
to the clutch cylinder 110.

[0037]As is obvious, there are many ways to embody the invention, which
only should be limited by the scope of the appended claims.